1. Field of the Invention
The present invention relates to a light emitting diode, in more particular, to a light emitting diode by which electrification at a large current with high efficiency can be realized.
2. Related Art
As for the light emitting diode, since full color light emitting diodes (LEDs) from red to blue have been achieved, application to lighting use is positively tried. However, it is necessary to solve two problems, in order to spread the light emitting diode for the lighting use. Firstly, it is necessary to increase a conversion efficiency of the light emitting diode from a level equal to that of an electric lamp to a level equal to a fluorescent lamp. Secondly, it is necessary to realize the electrification of one light emitting diode at the large current in order to obtain a brightness equal to the electric lamp or the fluorescent lamp by using a few light emitting diodes.
However, when the large current is flown into the light emitting diode, heat is generated, thereby deteriorating the conversion efficiency and the reliability. A first technique for avoiding this problem is to suppress the heat generation as much as possible, and a second technique is to dissipate the heat thus generated immediately to suppress a temperature elevation.
At first, in order to suppress the heat generation as much as possible, it is necessary to convert an electric energy into a light to be extracted as much as possible by increasing a light output efficiency of the light emitting diode. In order to increase the light output efficiency of the light emitting diode, it is necessary to increase an internal quantum efficiency that is an efficiency for recombining injected electrons and holes effectively as high as possible and to increase a light extract efficiency for extracting the emitted light from a LED chip.
Next, as techniques for dissipating the heat, for example, there is a technique for locating a light emitting layer which is a heat-generating part in vicinity of a mounting stem in order to dissipate the heat generated in the light emitting part to the mounting stem, and a technique for using a material with a low thermal resistance for a substrate provided between the light emitting layer and the mounting stem.
In general, the light emitting diode comprises an upper electrode (upper side electrode) having a large area at a light emitting surface, and an active layer included in the light emitting layer emits the light uniformly, so that the light emitted from the active layer in a region which is located right under the upper electrode cannot be totally extracted, due to the upper electrode.
As a light emitting device for avoiding this problem, Japanese Patent Laid-Open No. 2001-144322 (JP-A-2001-144322) and U.S. Pat. No. 6,784,462B2 disclose such light emitting devices, respectively. JP-A-2001-144322 discloses a light emitting device, in which an insulation layer for blocking a current flow is formed under the upper electrode. According to this structure, the current is dispersed in a periphery of the upper electrode, thereby suppressing the light emission right under the upper electrode.
In addition, U.S. Pat. No. 6,784,462B2 discloses a light emitting device, in which a partial electrode for providing an electrical conduction is disposed at a region other than the upper electrode.
However, according to the conventional light emitting diode, even though the device structure disclosed in JP-A-2001-14432 or U.S. Pat. No. 6,784,462B2 is applied, a conductive electrode is located under the light emitting part and a light absorption occurs in the conductive electrode as discussed above, so that a high light output efficiency cannot be realized.